--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const16.C	Thu Feb 13 11:34:05 2020 +0900
@@ -0,0 +1,22 @@
+// PR c++/91548 - fix detecting modifying const objects for ARRAY_REF.
+// { dg-do compile { target c++14 } }
+
+constexpr int& impl(const int (&array)[10], int index) {
+  return const_cast<int&>(array[index]);
+}
+
+struct A {
+  constexpr int& operator[](int i) { return impl(elems, i); }
+  const int elems[10];
+};
+
+constexpr bool
+f()
+{
+  A arr = {};
+  arr[2] = 1; // { dg-error "modifying a const object" }
+  return false;
+}
+
+constexpr bool b = f(); // { dg-message "in .constexpr. expansion of " }
+// { dg-message "originally declared" "" { target *-*-* } .-1 }